1. Field of the Invention
The invention relates in general to a touch control apparatus and an associated selection method, and more particularly to an optical touch control apparatus and an associated selection method.
2. Description of the Related Art
Based on different operation principles, touch control technologies may be categorized into capacitive touch technology, resistive touch technology and optical touch technology.
Among the above touch control technologies, the optical touch technology calculates coordinate of a position of a touch point through light shielding. The optical touch technology is easily applied to large-size applications and has lower production costs.
FIG. 1A shows a schematic diagram of a conventional optical touch control apparatus determining a touch point of a single object. In short, in an optical touch control apparatus, after lights are emitted from light machines (M1 and M2), an image sensor detects whether a touch point exists and coordinates of the touch point are further determined.
After infrared light is emitted from the light sources, a reflected light distribution at a position of an object O will be changed. At this point, the image sensor, cooperating with a controller, may calculate the position of the touch point according to changes in the reflected light distribution.
For illustration purposes, in the present context, an included angle formed by a connection line between the object O and the first light machine M1, and a fourth side IV of a display panel 14, is referred to as a left included angle θl. Similarly, an included angle formed by a connection line between the object O and the second light machine M2, and the fourth side IV of the display panel 14, is referred to as a right included angle θr. In the description below, it is assumed that sensors are disposed in the light machines. Thus, M1 is used to represent the first light machine/first sensor, and M2 is used to represent the second light machine/second sensor.
In FIG. 1A, according to a triangle formed by the position of the object O and the two light machines (M1 and M2), the controller may obtain an upper-left angle (the left included angle θl) and an upper-right angle (the right included angle θr) of the triangle. Coordinates of the touch point can then be calculated by a triangle function. The calculation of the position may be completed by real-time calculations, or may be obtained with a look-up table (hereinafter, LUT).
However, the conventional optical touch technology is inadequate in providing accurate touch points for multi-touch applications. When the number of the objects is plural, a conventional optical touch control apparatus may encounter confusions when determining the touch points due to different combinations of the left included angle θl and the right included angle θr.
When there are multiple objects, multiple left included angles θl and multiple right included angles θr are correspondingly generated. Numbers of the multiple left included angles and the multiple right included angles are defined in an increasing order. For example, a smallest left included angle is numbered as θl1, a smallest right included angle is numbered as θr1, and so forth.
When there are multiple objects, a connection line L between the objects and the first light machine M1 is represented according to the numbers of the left included angles. Similarly, a connection line R between the objects and the second light machine M2 is represented according to the numbers of the right included angles.
FIG. 1B shows a schematic diagram of a misjudgment on touch points by a conventional optical touch control apparatus when two objects exist on a display panel. In the diagram, it is assumed that a position of a first object O1 is P1, and a position of a second object O2 is P2.
Therefore, according to a triangle formed by the first object O1, the first light machine M1 and the second light machine M2, the second left included angle θl2 and the first right included angle θr1 can be obtained. Similarly, according to a triangle formed by the second object O2, the first light machine M1 and the second light machine M2, the first left included angle θl1 and the second right included angle θr2 can be obtained.
It can be concluded from the above, when two objects exist on the display panel 14, the sensors sense four included angles, i.e., the first left included angle θl1, the second left included angle θl2, the first right included angle θr1 and the second right included angle θr2.
When estimating touch points according to the first left included angle θl1 with the first right included angle θr1 and the second right included angle θr2, respectively, the controller obtains a candidate touch position F1 and a candidate touch position P2.
Further, when estimating touch points according to the second left included angle θl2 with the first right included angle θr1 and the second right included angle θr2, respectively, the controller obtains a candidate touch position P1 and a candidate touch position F2.
That is to say, the four candidate positions (P1, P2, F1 and F2) can be derived from combinations of the four included angles. However, the candidate touch position F1 and the candidate touch position F2 are not actual positions of the touch points.
The controller determines the above candidate touch positions according to positions of shadows replied from the sensors. When selecting two out of four, two of the shadows are false, and are referred to ghost points. These ghost points lead the controller to misjudge the actual positions of the touch points, as in the example above. Thus, the candidate touch position F1 and the candidate touch position F2 in FIG. 1B are ghost points.
As previously stated, when there are two touch points, the first sensor obtains two left included angles through sensing, and the second sensor also obtains two right included angles through sensing. Combinations of the two left included angles and the two right included angles form four candidate touch positions. By deducting the actual positions of the touch points from the four candidate touch positions, there are two ghost points.
As the number of touch points increases, the number of shadows (the candidate touch positions) obtained by the sensors also becomes larger, meaning that possibilities of misjudging ghost points as touch points also get higher.
For example, with three objects (in equivalence to three touch points on the display panel), the first sensor senses to obtain three left included angles, and the second sensor also senses to obtain three right included angles. Combinations of the three left included angles and the three right included angles form nine candidate touch positions. After deducting positions of the actual touch points, there are as many as six ghost points.
It can be deduced that, the number of candidate touch positions is substantially equal to a square of the number of objects. Therefore, as the number of objects increases, when designing an optical touch control apparatus, there is a need for a solution for quickly eliminating positions of ghost points from numerous candidate touch positions and to correctly select actual positions of touch points.